The instant invention generally relates to a signal compression circuit, particularly for telephone set, comprising a preamplifier, an input of which receives a signal to be processed and a preamplifier gain control device for servo-controlling, to a predetermined value, the amplitude of the output signal of the preamplifier.
A signal compression circuit can advantageously be integrated into the emission and reception channels of a telephone set, especially of the handsfree-type, that is, the apparatus is not fitted with a handset. The function of such a circuit in this type of apparatus is to compensate for the signal losses caused either by the distance existing between the speaker and the microphone when the apparatus is in the emission mode, or by the length of the line when the apparatus is in the reception mode.
Signal compression circuits have been used especially for reducing the noise during a magnetic recording. However, those circuits have a complex structure including in particular clocks and inverter circuits. Moreover, those circuits are of large sizes, are therefore cumbersome, need relatively high power voltages due to the use of CMOS technology, use current and have a relatively high price.
As a result of those various drawbacks, the compression circuits of the aforementioned type are unsuitable for being integrated into the emission and reception channels of a handsfree telephone set.
An object of the invention is to provide for a signal compression circuit adapted to telephone technology.
Another object of the invention is to provide for such a circuit adapted to solve a specific problem which is encountered when, in the emission mode, the gain control device of the preamplifier reacts to the noise between two speech peaks: Indeed, when a speaker starts speaking, it is essential that the preamplifier may quickly respond, however, it must not respond at the same speed between two speech peaks, as for example between two syllables, in order to avoid an unwished increase of the gain and therefore of the background noise.